Results of the ESO-SEST Key Programme on CO in the Magellanic Clouds X. CO emission from star formation regions in LMC and SMC

Abstract

We present J = 1−0 and J = 2−1 12CO maps of several star-forming regions in both the Large and the Small Magellanic Cloud, and briefly discuss their structure. Many of the detected molecular clouds are relatively isolated and quite small with dimensions of typically 20 pc. Some larger complexes have been detected, but in all cases the extent of the molecular clouds sampled by CO emission is significantly less than the extent of the ionized gas of the star-formation region. Very little di use extended CO emission was seen; di use CO in between or surrounding the detected discrete clouds is either very weak or absent. The majority of all LMC lines of sight detected in 13CO has an isotopic emission ratio I( 12CO)=I( 13CO) of about 10, i.e. twice higher than found in Galactic star-forming complexes. At the lowest 12CO intensities, the spread of isotopic emission ratios rapidly increases, low ratios representing relatively dense and cold molecular gas and high ratios marking CO photodissociation at cloud edges